CRISPR/Cas9 Ribonucleoprotein Nucleofection for Genome Editing in Primary Human Keratinocytes: Knockouts, Deletions, and Homology‐Directed Repair Mutagenesis

: Keratinocytes are the most abundant cell type in the human epidermis, the outermost layer of the skin. For years, primary human keratinocytes (HKs) have been used as a crucial tool for studying the pathogenesis of a wide range of skin-related diseases. To mimic the physiological and pathological behavior of human skin, organotypic 3D skin models can be generated by in vitro differentiation of HKs. However, manipulation of HKs is notoriously difficult. Liposome-mediated gene delivery often results in low transfection rates, and conventional electroporation results in high mortality, is difficult to optimize, and requires high cell numbers without necessarily achieving maximum efficiency. Additionally, HKs have a short lifespan in vitro, with a limited number of cell divisions before senescence, even when cultured on a feeder layer. Therefore, the possibility to use an efficient CRISPR/Cas9 system in HKs is not without challenge in terms of transfection technology and clonal selection. In this article, we provide detailed protocols to perform efficient gene knock-out (KO) or genomic deletion in a small number of HKs without clonal selection of edited cells. By nucleofecting ribonucleoprotein complexes, we efficiently generate KO cells as well as deletion of specific genomic regions. Moreover, we describe an optimized protocol for generating site-specific mutations in immortalized keratinocytes (N/TERT2G) by exploiting the homology-directed repair system combined with rapid single-clone screening. These methods can also be applied to other immortalized cells and tumoral cells of epithelial origin. Together, these protocols provide a comprehensive and powerful tool that can be used to better understand the molecular mechanisms underlying different skin diseases. © 2024 The Author(s). Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Knock-out generation by indel mutation in primary human keratinocytes using nucleofection of ribonucleoprotein (RNP) complex Basic Protocol 2: Deletion of specific genomic region using RNPs via nucleofection Basic Protocol 3: Use of homology-directed repair system to introduce site-specific mutations.